1. Field of the Invention
The present invention relates to gas turbines. More specifically, the present invention relates to an apparatus and method for cooling a gas turbine vane which prevents the plugging, by airborne particles, of cooling air passages in the vane.
2. Description of the Prior Art
A gas turbine is comprised of a compressor section for compressing air, a combustion section for heating the compressed air by burning fuel therein, and a turbine section for expanding the heated and compressed gas discharged from the combustion section.
The hot gas flow path of the turbine section of a gas turbine is comprised of an annular chamber contained within a cylinder and surrounding a centrally disposed rotating shaft. Inside of the annular chamber are alternating rows of stationary vanes and rotating blades arrayed circumferentially around the annular chamber. Hot gas discharged from the combustion section of the gas turbine flows over these vanes and blades. Since, to achieve maximum power output, it is desirable to operate the gas turbine so that this gas temperature is as high as feasible, the vanes and blades must be cooled. Cooling is obtained by causing relatively cool air to flow within and over the vanes and blades. To facilitate such cooling of the vanes, a hollow cavity is provided inside of each vane. The cavity is enclosed by the walls which form the airfoil portion of the vane. Cooling air enters the hollow cavity from an opening on the outboard end of the vane. The cooling air flows through the hollow cavity and then leaves the vane by flowing through holes in the walls of the vane enclosing the cavity. After discharging from these holes, the cooling air enters and mixes with the hot gas flowing over the vanes.
To adequately cool the vane it is necessary to guide the cooling air flowing through the cavity to ensure that it is properly distributed over the entire surface of the walls forming the cavity. This distribution is accomplished by installing a thin-walled vessel, referred to as an insert, into the cavity. After entering the vane, the cooling air flows into the insert and is distributed around the cavity by a plurality of small distribution holes dispersed throughout the insert.
Since to be effective the cooling air must be pressurized, it is bled from the compressed air discharged from the compressor. If the gas turbine is operating in a dirty or dusty environment, small particles entrained in the compressed air become deposited and accumulate in the small distribution holes in the insert, thereby plugging the holes. As a result, the ability of the insert to properly distribute the cooling air is impaired.
It is therefore desirable to provide an apparatus which will prevent plugging of the cooling air distribution holes in the vane insert.